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The user cannot establish a connection across a trunk link due to misconfiguration


Core issue

Improper Catalyst OS (CatOS) configuration results in the inability to establish a trunk link connection.


To resolve this issue, perform these steps:

  • If the user is unable to establish a connection across a trunk link, check the settings by issuing the set trunk command. 
  • Check the trunking mode configured on both ends of the link. The trunking mode should be on or desirable on one end, and on, desirable, or auto on the other end. 
  • Check the trunk encapsulation type configured on both ends of the link to ensure it is valid. 
  • Check that the port is trunking and that the allowed VLAN list allows the desired VLAN range to pass through. On IEEE 802.1q trunks, make sure the native VLAN is the same on both ends of the trunk. 
  • Verify that the port is capable of trunking by issuing the show port capabilities command.

For more information on these issues, refer to System Requirements to Implement Trunking.

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